Conventionally, there have been measured circuit parameters (such as the S parameters) of a device under test (DUT) (refer to a patent document 1 (Japanese Laid-Open Patent Publication (Kokai) No. H11(1999)-38054, for example)).
Specifically, a signal is transmitted from a signal source to a receiving unit via the DUT. The signal is received by the receiving unit. It is possible to acquire the S parameters and frequency characteristics of the DUT by measuring the signal received by the receiving unit.
On this occasion, measuring system errors are generated in the measurement due to mismatching between a measuring system such as the signal source and the DUT, and the like. These measuring system errors include Ed: error caused by the direction of a bridge, Er: error caused by frequency tracking, and Es: error caused by source matching.
On this occasion, it is possible to correct the errors as described in the patent document 1, for example. The correction in this way is referred to as calibration. A brief description will now be given of the calibration. Calibration kits are connected to the signal source to realize three types of states: open, short-circuit, and load (standard load Z0). In these states, a signal reflected from the respective calibration kits is acquired by a bridge to obtain three types of the S parameter corresponding to the three types of state. The three types of variable Ed, Er, and Es are acquired from the three types of the S parameter, and then are corrected.
It should be noted that Er is represented as a product of an error Er1 relating to an input of a signal, and an error Er2 relating to a reflection of the signal. On this occasion, it is possible to connect a power meter to the signal source to measure the power thereby measuring the errors Er1 and Er2 (refer to a patent document 2 (WO 2004/049564 pamphlet), for example).
The calibration described above can be applied to a switch branch signal source. It should be noted that the switch branch signal source is a combination of a signal source which generates a signal, and a switch which outputs the generated signal to any one of multiple ports. If the above calibration is applied to a switch branch signal source, three states including an open state, a short-circuit state, and a load state (with a standard load of Z0) will be realized for the respective multiple ports, and a power meter is also connected.